DB2中如何用sql语句实现下列功能

scooyy

我有两个sql查询语句：
语句1：select substr("Timestamp",2,6) as date, avg("AVG_Space_Used_Percent") as val  from  "Disk_DV"  where substr("Timestamp",2,6)   between '080501' and '080531'  and ("System_Name" like '%PEKII347%'  or "System_Name" like '%pekii347%') group by substr("Timestamp",2,6)  order by substr("Timestamp",2,6)

语句2：select substr("Timestamp",2,6) as date, avg("AVG_%_Used") as val from  "NT_Logical_Disk_DV"  where substr("Timestamp",2,6)   between '080501' and '080531'  and ("Server_Name" like '%PEKII347%'  or "Server_Name" like '%pekii347%')   group by substr("Timestamp",2,6)  order by substr("Timestamp",2,6)

我现在想实现当语句1执行失败的情况下，去执行语句2，请问在命令行中应该怎么写？请高人指点，谢谢。